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Kamal Singh Chamar

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Information about Kamal Singh Chamar
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Published on August 6, 2009

Author: aSGuest23546

Source: authorstream.com

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APPLIED ANATOMY OFVISUALANDGUSTATORY PATHWAYS : APPLIED ANATOMY OFVISUALANDGUSTATORY PATHWAYS Slide 2: Clinical comments:- Lesions of visual pathway:- Injury to any part of visual pathway produces defects in vision, whose nature depends on the location and extent of injury. The defects are described in terms of visual fields. Loss of vision in on half (right or left) of the visual field is called hemianopia: if the same half of visual field is affected in both the eyes, the defect is called homonymous hemianopia; but if different halves are affected the defect is known as anterior to LGB also damages the fibres responsible for papillary light reflex. Slide 3: Lesion:- Right optic nerve. Defect:- (i) Total loss of vision in right eye (anopia), (ii) when light is thrown into the affected eye there is loss of light reflex in both eyes; but consensual light reflex is present in the affected eye. Lesion:- Optic chiasma in midline due to pressure from a pituitary tumour. Defect:- Bitemporal heteronymous hemianopia i.e., loss of temporal halves of fields of vision of both eyes. Lesion:- Both edges of optic chiasma. Defect:- Binasal heteronymous hemianopia i.e. loss of nasal halves of fields of vision of both eyes. Lesion:- Right optic tract. Defect:- Left homonymous hemianopia i.e., loss of left halves of fields of division of both eyes. Lesion:- Right optic radiation or visual cortex. Defect:- Left homonymous hemianopia with sparing of macular vision. Note:- Visual defect in one quadrant will give rise to quadrantic hemianopia. Slide 5: Visual reflexes include: (i) Light reflex (ii) Accommodation reflex (iii) Spino-visual reflex. Light Reflex:- Definition:- When a beam of light is thrown into one eye pupils of both eyes constrict. Types:- (a) Direct light reflex: is constriction of pupil into which light reflex: is the constriction of opposite pupil. Pathways: - Affrent path:- Impulss from retina –optic nerv –optic chiasma –optic tract-prtectal nuclei of both sides- Edinger Westphal nucleus of both sides. Efferent path:- Preganglionic fibrs from E.W. nucleus pass through 3rd cranial nerve and its branch to inferior oblique to ciliary ganglion; pastganglionic fibrs arising from the ganglion transverse short ciliary nerves to reach sphincter pupilae. Slide 6: Accommodation Reflex:- Definition:- The process by which an image is kept in sharp focus, when the gaze is shifted from a far object (beyond 40 cm) to a near object is called accommodation. Changes in accommodation:- Constriction of pupil to increase the depth of focus, Thickening of lenses to increase refractive index; this is due to contraction of ciliary muscles, and Convergence of eyes, caused by contraction of medial recti muscles. Pathways: Afferent path:- Impulses from retina by way of optic nerve-optic tract-lateral geniculate body and optic radiation to visual cortex. Central connections:- From occipital cortex fibres pass by way if superior longitudinal fasciculus to eye field of frontal cortex; from here the fibres descend through the internal capsule to the oculomotor nuclei in midbrain including Edinger Westphal nuclei. Efferent path:- Fibres arising from oculomotor nucleus supply medial recti muscles. Preganglionic fibres arising from Edingr Westphal nucleus -3rd cranial nerve-branches to inferior oblique - relay in ciliary ganglion: postganglionic fi8bres supply sphincter pupillae and ciliary muscles. Slide 8: Argyll Robertson pupil:- is characterized by small pupil of fixed size, which does not react to light but reacts with accommodation. The pupillo-constrictor pathways for light reflex and accommodation are separate. In tables dorsalis the pupil light reflex is lost, but pupil constriction as a part of accommodation is present. This phenomenon is Argyll Robertson pupil. The site of lesion lies between the Edinger Westphal nucleus aznd the lateral geniculate body, where the pathways for the two reflexes diverge from each other. Spino-visual Reflxes:- Definition:- Spinovisual reflexes are concerned with coordinated movements of eyes, head and neck in response to visual stimuli. These responses include turning the eyes (conjugate deviation) and head towards the visual stimuli, together with closing the eyelids and perhaps raising the arms to further protect the eyes. Pathways:- Afferent path:- Impulses from retina-optic nerve-optic tract-superior colliculus. Central connections:- Two tracts arise from superior colliculus: tctobulbar and tactospinal tracts. The tectobular tract terminates in the brainstem reticular formation and connects 3rd, 4th & 6th cranial nerved nuclei; the tectospinal tracts at ends on the spinal accessory nucleus and the anterior horn cells of spinal cord, especially of the cervical region. Efferent path:- Axons from 3rd, 4th 6th and spinal accessory nuclei pass to eye and neck muscles. Thus co-ordinated movements of the head, neck and eyes occur in response to visual stimuli. GUSTATORY (TASTE) PATHWAYS : GUSTATORY (TASTE) PATHWAYS Receptors: Taste buds are the receptors for taste. The facial (VII) nerve supplies taste buds on the anterior 2/3 of the tongue (excluding vallate papillae) and the soft palate; the glossopharyngeal (IX) nerve supplies the posterior 1/3of the tongue including the vallate papillae; and the vagus (X) nerve supplies the extreme posterior part of the tongue and the epiglottis. Slide 12:  Afferent neuron: The cell bodies (unipolar) are located in the geniculate ganglion of VII nerve and the inferior ganglia of IX and X cranial nerves. The central processes of these ganglion cells enter the brainstem and form the tractus solitarius which ends in the upper part of the nucleus of tractus solitarius. Second order fibres arising from the solitary nucleus cross to opposite side and ascend as solitario-thalamic tract, in the dorso-medial part of medial lemniscus to terminate in the ventral posteromedial nucleus of the thalamus and probably in the hypothalamus. Third order fibres from the thalamus pass via internal capsule to the lowermost part of postcentral gyrus of cerebral cortex and to adjacent insular cortex.

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